1. Field of the Invention
The present invention relates to a manufacturing method of a pneumatic tire in which a line, a letter or the like having a different color from a main body rubber is formed in a side wall portion.
2. Description of the Related Art
Conventionally, there has been known a pneumatic tire in which a line or a letter such as a maker logo having a different color from a main body rubber is formed in a side wall portion for the purpose of improving a fashion property. The pneumatic tire mentioned above can be manufactured, for example, by using a raw tire shown in FIG. 8. In FIG. 8, a white rubber layer 8 having a different color from a main body rubber is arranged in a side wall portion 31 of a raw tire, and a thin cover rubber layer 9 having the same color as the main body rubber is arranged in an outer side of the white rubber layer. The line, the letter or the like can be formed by vulcanizing the raw tire, thereafter scraping a predetermined region of the cover rubber layer 9 and exposing the white rubber layer 8 (refer to Japanese Unexamined Patent Publication No. 9-1694). Further, there has been known a method of vulcanizing by using a mold having a predetermined inner surface shape and protruding a predetermined region as shown in FIG. 9 in such a manner as to prevent the portion from which the cover rubber layer 9 is scraped from being formed in a groove shape. In accordance with the method mentioned above, it is possible to form the line, the letter or the like in an approximately flat surface by scraping a protruding portion 32 (refer to Japanese Unexamined Patent Publication No. 10-222070).
On the other hand, as a forming method of a side wall member structuring a side wall portion, there has been conventionally known a method in accordance with an extrusion molding, and a method in accordance with a ribbon winding. The formed side wall member is attached to a carcass ply wound around a drum together with the other rubber member. The raw tire can be formed by deforming the carcass ply along a tire shape and attaching a tread member.
In accordance with the former method, the side wall member can be formed by using an extruding machine and a molding die, extruding a rubber composition in a cross sectional shape of the side wall portion, and cutting at a predetermined length. However, in accordance with the method, it is necessary to prepare a lot of side wall members having various widths in order to correspond to each of the tire sizes, and it is necessary to prepare the side wall members having the white rubber layers of the respective widths in order to correspond to each of the sizes of the different color portions such as the line. As a result, there is a problem that the number of parts of the side wall member is increased. Further, it is necessary to change a stage such as a position adjustment every time of changing the tire size, and a productivity is lowered. In addition, since a step or the like is generated in a joint portion of the rubber member, a uniformity of the tire is lowered.
In accordance with the latter method, the side wall member is formed by spirally winding a rubber ribbon (a rubber strip) with an overlap in a tire peripheral direction (refer to Japanese Unexamined Patent Publication No. 2002-79590, Japanese Unexamined Patent Publication No. 2002-200677 and a pamphlet of International Publication 02/060676). Alternatively, the side wall member is formed by winding the rubber ribbon around an outer peripheral side of a formed product obtained by an extrusion molding (refer to Japanese Patent No. 3370282). Subsequently, each of the white rubber layer and the cover rubber layer is formed by winding the rubber ribbon around the outer periphery of the side wall member. However, in accordance with this method, it is hard to form the cover rubber layer thin at a uniform thickness. As a result, there is a problem that the white rubber layer is not uniformly exposed at the time of scraping the vulcanized cover rubber layer by a buff or the like, and a strain is generated on the buffed surface. This problem is significant in the case that a predetermined region of the cover rubber layer 9 is protruded as shown in FIG. 9. Further, since the rubber ribbon having a small cross sectional size is wound several times over, it takes a long time to form the tire, so that there is a problem that a productivity is lowered.